All hay contains some mold. But when mold becomes easily noticeable, livestock producers can face some tough decisions, says Bruce Anderson, forage specialist with University of Nebraska Extension.

“Usually, mold makes hay less palatable, which can result in lower intake or even in animals refusing to eat the hay,” says Anderson. “Many other problems from mold occur because of mycotoxins produced by certain mold fungi. This also is part of the decision problem since not all molds produce mycotoxins, and the amount produced by those that do is unpredictable.”

It’s difficult to document the direct negative effects of moldy hay. Horses may be sensitive to it, and mold spores often contribute to respiratory and digestive problems like colic or heaves in horses. Cattle apparently are less affected by mold, but certain molds can cause mycotic abortions or aspergillosis.

The best course of action often is to minimize feeding moldy hay to more sensitive animals, like horses or pregnant cows. “This may require a keen eye or sensitive nose when selecting hay to feed each day,” says Anderson. “Mixing moldy hay with other feedstuffs can dilute problems sometimes. But be careful that you don’t make your animals sick by tricking them into eating bad hay they normally would refuse.”

People handling moldy hay need to be careful too, Anderson says. “Mold can cause a condition called farmer’s lung, where the fungus (from mold spores) actually grows in lung tissue. So try to avoid breathing in many of these spores.”